Of course Biogen is spending money on advertising ALL of their drugs! But Novartis is spending money on an extensive ad campaign for just Gilenya. From the link:
"[T]he drugmaker recently began pushing an aggressive advertising campaign aimed at younger patients and also began sponsoring lunches at restaurants around the country where patients and caregivers can learn more about its pill."
The New York Times even wrote about it as well: http://www.nytimes.com/2013/04/04/business/media/an-ms-drug-takes-a-feisty-approach-aimed-at-younger-patients.html?_r=0
I haven't seen Teficdera advertised anywhere outside of MS-related magazines.
As far as Tysabri is concerned, Biogen withdrew it from the market shortly after 3 people developed PML during a Phase III trial: http://en.wikipedia.org/wiki/Natalizumab#Legal_status
It was MSers who petitioned the FDA to bring it back because they were willing to take the risk of PML to get the benefits: http://www.nytimes.com/2006/03/09/business/09drug.html?_r=1&scp=2&sq=natalizumab&st=nyt&oref=slogin
And haven't you seen their current ads? They're not hiding the fact that PML is a risk of Tysabri in the fine print.